1) Crystals of the Rnase H from HIV have been investigated. The crystals diffract to about 3.5A resolution. Many heavy atom derivatives have been examined in order to provide an interpretable electron density map. 2) Crystals obtained of the OKT4A/CD4 complex have been grown to X-ray dimensions. Examination of these crystals showed that they do not diffract to atomic resolution. The crystallization conditions for the HIV integrase protein are being investigated.